bug#18195: 24.3.92; window-screen-lines is not accurate

[martin rudalics <rudalics@gmx.at>]

 > He can't: we currently don't expose enough information for Lisp
 > programs to perform layout.  E.g., the metrics of glyphs and lines
 > that use arbitrary fonts and display images are not easily available
 > on the Lisp level, and neither are dimensions and line counts of
 > arbitrary regions of the screen (although you could write some clunky
 > Lisp to do the latter).  Likewise with dimensions of text in overlays
 > and display properties, and with images.
 >
 > This was never supposed to be needed, and thus was never designed and
 > implemented.  If we want to allow such jobs from Lisp, we need to
 > close these gaps.

Why would `window-text-pixel-size' fail to provide that?  It might be a
bit clumsy to work with because you have to temporarily show another
buffer in its window but apart from that I see no problems ...

martin